Summary On 20 March 2004, the Baby Belle amateur-built helicopter (registration C-FZQN, serial numberBB2066) departed from a farm located near Ralph, Saskatchewan, on a local visual-flight-rules flight. The purpose of the flight was to inspect grid road and highway intersections for snow accumulation. Shortly after take-off, debris began to fall from the helicopter while it was flying in a northwesterly direction at approximately 500feet above ground level. The helicopter dropped vertically; the nose pitched down; and the helicopter, while in a steep, nose-down attitude, crashed on a farm field. The pilot, the sole occupant, was fatally injured. The helicopter was destroyed by a post-impact fire. The accident occurred at approximately 1000central standard time. Ce rapport est galement disponible en franais. Other Factual Information The pilot held a valid private pilot helicopter licence with Baby Belle and RH22 endorsements, daylight only, and was properly certified for the intended flight. The pilot, who also constructed and maintained the helicopter, had a total of 208hours of flight time, of which 137hours were on type. The helicopter was an amateur-built aircraft constructed from a kit. Construction was completed in2003, and the helicopter had a total flight time of 169hours. The closest meteorological reporting office was at the Regina Airport, approximately 75miles northwest of the accident site. At 1000 central standard time,1 the weather recorded at the Regina airport was as follows: ceiling unlimited, visibility 15statute miles, temperature -10C, wind 350at 11knots gusting to 16 knots, and altimeter setting30.60. The meteorological conditions were similar at the accident site, where they were reported as clear with strong, gusting northwesterly winds. The helicopter struck the ground at a steep angle. Fuel samples and instrument readings were not available because of the post-impact fire. The main rotor blades had separated from the main mast yoke and were found at the main wreckage site. Indentation marks on the yoke were consistent with mast bumping, and the main rotor blades exhibited extensive downward bending. The spar of one rotor blade had failed in overload. Damage to the engine cooling fan, which is driven by the engine, was consistent with little or no engine power at the time of impact. The flight controls were inspected, and no pre-impact anomalies were found. Several searches of the accident site and the surrounding area were conducted. Scattered pieces of the bubble canopy and 4130-tubular-steel tail boom structure were found one-half kilometre from the main wreckage. Station 214-241of the tail boom structure, with the tail rotor gear box still attached to its mount, was found 40metres from the main wreckage. The tail rotor, which had separated at the gear box shaft, was found approximately 100metres from the main wreckage. Analysis of the fractured shaft revealed an overload failure. The horizontal stabilizer attachment structure (seePhoto1) had broken off the tail boom and was found adjacent to station 214-241of the tail boom structure. The attachment structure had a piece of stabilizer spar still attached. This piece of horizontal stabilizer spar revealed a complete fracture at the first rivet hole of the root end. Despite several searches of the area under and surrounding the flight path, the horizontal stabilizer airfoil was not found. Analysis of the fracture revealed 75percent fatigue cracking around the circumference of the spar tube (seePhoto2). The remainder of the spar tube had failed in overload. Although the horizontal stabilizer airfoil was not found, the horizontal stabilizer was still attached to the helicopter at the conclusion of the previous flight. Photo1. Horizontal stabilizer attachment structure and spar section Photo2.Horizontal stabilizer spar fracture The horizontal stabilizer is a 22-inch long symmetrical airfoil mounted with a 2-degree positive angle of incidence, opposite the tail rotor at station241 (seeAppendixA). The horizontal stabilizer is constructed of 4130-steel spar tubing and has holes drilled through it for attaching the airfoil with rivets. In forward cruise flight, the stabilizer aids in controlling the helicopter. At speeds below 70mph, the stabilizer lifts the tail. At speeds above 70mph, it forces the tail downward. At speeds above 70mph, the slipstream acts upon the bubble canopy, pitching the nose down and the tail up. As the tail pitches up, the top surface of the horizontal airfoil engages with the slipstream, resulting in a downward force to achieve an equilibrium. The stabilizer also dampens vibrations caused by the tail rotor. The horizontal stabilizer attachment structure found at the site was equipped with an aluminum end cap that was mounted against the airfoil at the root end (seePhotos1and2). A review of the construction drawings and a discussion with the kit manufacturer, revealed that the stabilizer is equipped with an end cap on the outboard end of the airfoil and is not designed with an end cap at the root end. The helicopter had previously been subject to a tail-rotor blade separation and two tail-rotor strikes during hovering manoeuvres. A review of the maintenance records indicated that the tail rotor had been replaced 111 flight hours prior to the accident flight. No record of any tail-rotor strike was found. The Canadian Aviation Regulations require that the particulars of any abnormal occurrence involving an aircraft be recorded in the aircraft journey log. The tail-rotor blade separation that occurred previous to the accident flight caused the horizontal stabilizer spar to bend. The spar was subsequently bent back and cold straightened using a press. This process for straightening a tubular horizontal stabilizer spar is not a recommended maintenance practice. No record of the spar repair was found in the aircraft maintenance records.